Keyboards are used as the communication medium between electronic equipment and the user of the equipment. Keyboards allow the user to manually input data and/or command electronic equipment to function in a particular manner. The most widely used modern keyboards come in two general varieties. One variety is flat and the keys are selected regions of an overlay. When pressure is applied to a "key" overlay region, a switch mechanism located beneath the overlay region is actuated. Actuation of the switch is detected by the associated electronic equipment and causes the equipment to function in a particular manner. The other variety of modern keyboards includes discrete key elements mounted in or surrounded by a bezel--a plate having holes through which the key elements pass. The depression of a key element causes the actuation of an underlying switch mechanism, which is detected by the associated electronic equipment. The present invention is directed to discrete key element keyboards, which are sometimes referred to as "full throw" keyboards by virtue of the fact that the travel distance of the discrete key elements is substantially greater than the travel distance of the key overlay regions of flat keyboards.
Discrete keyboards can be broken into two general types--those in which the keys have a straight up-down path of travel, and those in which the keys have an arcuate path of travel. Arcuate path of travel keys are hinged along one edge in some manner. Regardless of their path of travel, both types of keys move an underlying element when they are depressed. The underlying element makes contact with one or more further elements to "close" a switch.
In many prior keyboards, the movable underlying element actuated when a key is depressed is a metal dome that collapses when impacted by a sharp point formed on the underside of the depressed key. More recently, the metal dome "keypads" used in some keyboards have been replaced with elastomer dome keypads, which are considerably less expensive to produce. Elastomer dome keypads include a layer of elastomeric material having domes located at predetermined positions. Locationed in the center of the domes is a piece of conducting elastomer. Collapsing a dome causes the conducting elastomer to contact switch elements formed on the surface of an underlying printed wire board.
Prior to the present invention, elastomer dome keypads have been primarily used in keyboards in which the keys have a straight up-down path of travel. Elastomer dome keypads have not been used in keyboards in which the keys have an arcuate path of travel. Thus, the lower cost benefits resulting from the use of elastomer dome keypads have not been implemented in arcuate or "rocker" type keyboards.
The primary reason why elastomer dome keyboards have not been implemented in rocker-type keyboards is due to the fact that the arcuate path of travel followed by the keys of such keyboards does not allow an elastomer dome keypad to be readily substituted for a metal dome keypad, as has been the case with straight up-down path of travel keyboards. The reason why elastomer dome keypads cannot be readily substituted for metal dome keypads in rocker-type keybaords is due to the fact that the domes of elastomer dome keypads collapse in an entirely different manner than the metal domes of a metal dome keypad. Straight up-down movement presses a large flat surface against an elastomer dome which is the ideal way of collapsing the center region of an elastomer dome and creating positive contact between the conductive elastomer and the underlying switch elements. An arcuate path of travel tends to collapse one side rather than the center region of an elastomer dome resulting in less than ideal contact between the conductive elastomer and the underlying switch elements.
Another disadvantage of prior rocker-type keyboards including metal dome keypads is the complexity of the rocker mounting structure. More specifically, metal dome keypads, as compared to elastomer dome keypads, require high actuation force from the keys. As a result, a relatively rugged key mounting structure is required. One common mounting mechanism involves hinging the rocker-type keys on wire guides mounted on standoffs affixed to the printed wire board containing the switch elements that are contacted when a metal dome is collapsed. Since rods and standoffs are expensive, the cost of keyboards using such mechanisms is undesirably high. Further, unacceptably high numbers of breakage problems occur where the key grabs the rod. Also assembly time is high because keys must be attached to the hinge rods before other portions of the keyboard are assembled. Finally, the rods and standoffs require a significant amount of room, which makes the distance between keys greater than desirable.
This invention is directed to providing rocker key elastomer dome keyboards that are inexpensive to produce and avoid the cost and other disadvantages of rocker-type keyboards that employ metal dome keypads.